1. Field of the Invention
This invention in general relates to illumination devices and in particular to a lighting device for uniformly illuminating a transparency, such as a 35 mm color slide, for photocopying or projection purposes.
2. Description of the Prior Art
Devices for illuminating transparencies (e.g., 35 mm slides) for projection onto a viewing screen or onto film for photocopying are well-known in the prior art. Such illumination devices must not affect the definition of the final image and must, more or less, uniformly illuminate the transparency. Commonly, such devices comprise an illumination source, an associated concave reflector, and a condenser type optical system which operates to increase the efficiency of the system and to improve the evenness of illumination. To this end, the known condenser systems, which may comprise one or more lenses, usually image the source in the pupil of a projection lens so that the lens aperture has the same brightness as the source while the projection lens images the transparency, positioned between the condenser system and the projection lens, on the viewing screen or film used for photocopying.
Another type of known lighting device for evenly illuminating transparencies includes a housing and a mercury discharge lamp having a multiple coiled tube situated in the housing immediately adjacent an opal glass diffuser. However, the mercury discharge type lamp is unsuitable for color copying because of its spectral content.
Of the known transparency illumination devices, the condenser type is somewhat complex because it requires an auxiliary optical system while the mercury discharge lamp type is unsuitable because of its spectral content. Consequently, it is a primary object of the present invention to provide a simple lighting device for uniformly illuminating color transparencies for photocopying purposes.
It is another object of the present invention to provide a lighting device having only one source and a simplified reflector by which transparencies can be substantially uniformly illuminated for photocopying purposes or projection purposes.
Other objects of the invention will, in part, be obvious and will, in part, appear hereinafter. The invention, accordingly comprises the apparatus possessing the construction, combination of elements, and combination of parts which are exemplified in the following detailed disclosure.